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What are some general features of the extracellular environment?
- Cells receive nourishment from and release wastes into this.
- Cells communicate with each other by secreting chemical regulators into this.
Discuss body fluid proportions.
- 67% of water is within the intracellular compartment.
- 33% of water is in the extracellular compartment.
- -20% in blood plasma
- -80% makes up interstitial fluid, which connects the intracellular compartment with the blood plasma.
Describe the extracellular matrix
- Contains fibers of collagen and elastin, and a gel-like ground substance.
- a. Protein fibers provide structural support.
- b. Ground substance is composed of glycoproteins and proteoglycans.
- c. Integrins are glycoproteins that extend from the cell cytoskeleton and bind to the extracellular matrix.
What are the functions of integrins?
- a. Impart a polarity to cells.
- b. Affect adhesion and motility.
- c. Affect proliferation.
Plasma membrane transport
- 1. Plasma membrane permeability
- a. The plasma membrane is selectively permeable, meaning that it allows some molecules to cross but not others.
- b. Generally not permeable to proteins, nucleic acids, or other large molecules.
- c. Generally permeable to ions, nutrients, and wastes.
Describe types of noncarrier-mediated transport.
- 1. Simple diffusion of lipid-soluble molecules.
- 2. Simple diffusion of ions through nonspecific channels.
- 3. Simple diffusion of water (osmosis).
Describe types of carrier-mediated transport.
- 1. Facilitated diffusion.
- 2. Active transport (requires ATP)
- 3. Energy involvement in membrane transport.
What are the differences between passive and active transport?
Passive transport: molecules move from higher to lower concentration without using metabolic energy.
Active transport: molecules move from lower to higher concentration using ATP and specific carrier pumps.
The random motion of molecules caused by a concentration difference between two regions.
-Obeys second law of thermodynamics: diffusion increases entropy.
Will occur without a physical separation or across a permeable membrane.
Net diffusion: due to random movement, the net direction of diffusion is from high to low solute concentration.
- Mean diffusion time: the average time it takes for particles to diffuse & reach equilibrium.
- -Increases with the square of the distance the solute must travel (less distance = faster).
- -Distances beyond 100 µm, diffusion time is toooooo long to be effective.
Discuss diffusion through the plasma membrane.
- Because the plasma membrane is a bi-lipid layer, molecules that are small, nonpolar or uncharged, or lipid-soluble pass easily through it. These include:
- -Oxygen, carbon dioxide, and stereoid hormones.
Gas exchange: net diffusion of O2
into cells and CO2
out of cells due to concentration gradients (opposite in lungs).
Water can pass through awesome channels known as aquaporins
Charged ions pass through ion channels that cross the plasma membrane that may always be open or gated
Larger polar molecules can not
pass through the membrane by simple diffusion, but need special carrier proteins.
What is the rate of diffusion?
A measurement of the number of diffusing particles per unit time.
- This is determined by:
- 1. The steepness of the concentration gradient.
- 2. Permeability of the membrane to the molecules.
- 3. Temperature of the solution (high temp increases the rate).
- 4. Surface area of the membrane (which can be increased by structures like microvili).
What are some characteristics of osmosis?
Because water molecules do not carry a charge, so they can pass through the plasma membrane slowly.
- This is the diffusion of solvent instead of solute, it is unique.
- -Aided by channels in the membrane called aquaporins.
- -Many aquaporins are found in the kidneys, eyes, lungs, salivary gland and the brain.
What are requirements of osmosis?
There must be a concentration difference on either side of a membrane permeable to water.
- This membrane must be impereable to the solute, or the conc. difference will not be maintained.
- -Solutes that cannot cross and permit osmosis are called osmotically active.
How does water move in osmosis?
The net movement of water is from the sidewith more water (more dilute) to the side with less water (less dilute).
- However, when osmosis is discussed, we say that water moves from the area of low solute to the area of high solute.
- -Water moves toward the side with the higher solute concentration.
What is osmotic pressure?
This refers to the force surrounding a cell required to stop osmosis.
- Can be used to describe the osmotic pull of solution. A higher solute concentration would require a higher osmotic pressure.
- -Pure water has an osmotic pressure of 0.
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